The author poses a question: when a person has a thought, what is it that determines what thought he is having? and, equivalently, what is it that determines what thought he is having. looking for an answer he sketches some general aspects of the problems involved in answering these questions, like the mind/body problem, for example. his conclusion is that the posed questions should be set against the background assumption that thoughts are just internal physical occurrences, and that thoughts are categorized in the same way other mental occurrences are categorized. so the author categorizes them in terms of their introspectible characteristics and in terms of "that" clauses. these classifications can be understood as describing thought in terms of their place in the rational architecture